For decades the power equipment industry has been working on ways of reducing the hazards associated with power mowers and other like equipment having blades which operate at high speeds. Despite this effort, the Consumer Products Safety Commission has found it necessary to require that all walk behind lawn mowers manufactured after June 30, 1982 be designed so that the mower blade will stop within three seconds after the operator's hands have been removed from the handle. To accomplish this, there are two general approaches that may be used. One involves stopping the engine by means of an automatic switch or the like which is activated upon release of the handle. While effective, this approach is troublesome and wasteful as it necessitates frequent re-starting of the engine.
The other approach, which involves use of a brake and clutch system which will stop the blade and yet allow the engine to keep running, is a more desirable way to proceed. However, in practice it has been found very difficult to devise a system which is simple, inexpensive and highly effective.